title: Vitamin D supplementation and risk of respiratory tract infections: a meta-analysis of randomized controlled trials.
abstract: BACKGROUND
  It is well-documented that serum levels of 25-hydroxyvitamin D (25-OHD) are inversely associated with the risk of respiratory tract infections (RTIs). However, whether or not vitamin D supplementation prevents RTIs remains inconclusive. The aim of this study was to evaluate the role of vitamin D supplementation in preventing RTIs in healthy populations by performing a meta-analysis of randomized controlled trials (RCTs).
  
  
  METHODS
  RCTs regarding the association between vitamin D supplementation and the risk of RTIs were identified by searching PubMed, Embase, and Cochrane databases through January 2013. Reference lists of retrieved articles were also reviewed. Either a fixed-effects or, in the presence of heterogeneity, a random-effects model was used to calculate the pooled preventive effects.
  
  
  RESULTS
  Seven RCTs involving 4827 participants were included in this meta-analysis. The pooled relative risk (RR) for subjects administered with vitamin D compared with control groups was 0.98 (95% confidence interval 0.93-1.03, p = 0.45). Meta-regression analyses showed almost no impact on the RR of age, vitamin D dosing regimen, and length of follow-up. Omission of any single trial had little impact on the pooled risk estimates. No evidence of publication bias was observed.
  
  
  CONCLUSIONS
  Our findings do not support the routine use of vitamin D supplementation for RTI prevention in healthy populations. Larger studies are needed to investigate the effects of vitamin D supplementation on RTI prevention in various populations and to further clarify the influences of age, vitamin D dosing regimen, baseline levels of vitamin D, and study length.
authors.affiliation: Department of Nephrology, Nanjing Children's Hospital of Nanjing Medical University, Nanjing, China.
authors.forename: Song
authors.initials: S
authors.lastname: Mao
authors.forename: Songming
authors.initials: S
authors.lastname: Huang
mesh_terms: D019587:Dietary Supplements / Q000706:statistics & numerical data*; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D012141:Respiratory Tract Infections / Q000188:drug therapy / Q000453:epidemiology* / Q000517:prevention & control; D014807:Vitamin D / Q000008:administration & dosage*
chemical_list: D014807:Vitamin D